Self-expanding stents, particularly those made from the shape-memory alloy Nitinol, are well known in the art of intravascular stents. These stents are typically placed within a sheath-like stent delivery system for placement into a stenosis of a vessel such as an artery of a human body. When the sheath of the stent delivery system is pulled back, the self-expanding stent will deploy radially outward against the wall of a vessel of a human body such as a coronary artery. After they are deployed, it is typically necessary to remove the sheath-like catheter that delivered the stent and then insert a balloon angioplasty catheter for the purpose of further expanding the stent at the site of an arterial stenosis. This results in additional time and cost for performing this procedure. The balloon that is used for further expansion of the stent is typically longer than the stent itself. Therefore, the regions of the artery just beyond the distal and proximal edges of the stent undergo some trauma caused by the expansion of the balloon. This trauma caused by the balloon expansion beyond the stent edges also occurs with balloon expandable stents.
One disadvantage of existing delivery systems for self-expanding stents (i.e., sheath-like catheters) is that they have a larger diameter as compared to a stent delivery system that does not use a sheath. Another disadvantage is that they have less flexibility and are therefore more difficult to deliver into highly curved arteries such as the coronary arteries. All stent delivery systems that have an expandable balloon extending beyond the edges of the stent can cause an "edge effect" which is a narrowing of the artery just beyond the edges of the stent. The edge effect is particularly pronounced when a radioisotope stent is placed into an arterial stenosis. Still another disadvantage of using a sheath to deploy a self-expanding stent is that it is more difficult to exactly position the stent within a stenosis as compared to the accurate positioning that is achievable with balloon expandable stents.
Because balloon expandable stents have the inflated balloon extending beyond the edges of the stent, arterial wall edge dissections are sometimes encountered. These dissections typically require an additional stent implantation to repair the dissection in order to decrease the possibility that acute or subacute thrombosis or restenosis will occur.